Synthesis of IR-sensitive photoswitchable molecules: photochromic 9 '-styrylquinolinedihydroindolizines

New mono-(5a-t, w) and biphotochromic (5u, v) 9'-styrylquinolinespirodihydr oindolizines (DHIs) with IR-absorbing colored forms (4) were prepared. The conformation and configuration of these new DHIs were investigated by NMR s tudies and the structure was proved by x-ray analysis. The kinetics of the fast cyclizing process of betaine 4 to DI-II 5 takes place in the milliseco nd range and were studied by flash photolysis. The absorption bands of the betaines 4 were recorded at low temperature by FT-UV/VIS/near-IR spectrosco py. Large solvent effects on the absorption maxima of betaines 4 were obser ved. Copyright (C) 2000 John Wiley & Sons, Ltd.